Biological Approach 1: Anatomy, Physiology, Genes

Amygdala

Fear/stress responses, high amygdala activation relates to high neuroticism

Frontal Cortex

Long term planning, inhibition of impulses, very active prefrontal cortex means high conscientiousness

Hippocampus

Memory

Neural bases of personality

1. Brain damage

2. Brain stimulation

3. Brain activity and imaging

Brain damage

• patients with brain lesions caused by accidents/disease or placing lesions in animal brains (rats, dog, monkeys)

• Damage to frontal cortex means —> increased impulsivity and poor self control

Brain stimulation

Stimulates parts of the brain directly with electrodes

Brain activity and imaging

• detecting temporal patterns

• Detecting locational patterns

Temporal patterns

When the brain is working

What tests are good for detecting temporal patterns

Electroencephalography (EEG), Magnetoencephalography (EEG) [brain waves]

Locational patterns

Where the brain is working

What tests are used for detecting locational patterns

Computed tomography scans (CT scan), Positron Emission Tomography (PET), Functional Magnetic Resistance Imaging (fMRI) [see which areas of the brain are active]

What neural system is correlated with extraversion

Approach system (sensitivity to reward)

What neural system is correlated with agreeableness

Care system (long term bonds, understanding others’ thoughts, feelings, and behaviors)

What neural system is correlated with conscientiousness

Self regulation system (standards/control, execution of planned actions)

What neural system is correlated with neuroticism

Avoidance/vigilance system (sensitivity to punishment)

What neural system is correlated with openness to experience

Explore system (interests) — least identified neural correlates

Caveats

• personality not a specific place in the brain

• All parts of the brain are always active to some degree

• Compares between mean levels of brain activation, not precise patterns of brain activation

• Multiple comparisons lead to false positives, especially with small sample sizes

Neurotransmitters

1. Electrical impulse causes neurons to release NT chemicals into synapse

2. NT’s fit into receptors

3. Presence of the NT’s in the receptor promotes or inhibits the transmission of an electrical impulse down the lengths of the neuron toward the next synapse in the chain

Synapse

Gap between one neuron and the next

Receptors

Specially shaped molecules on the neighboring neuron

Dopamine

• involved in responding to reward

• Approach (“go”) system (extraversion and openness)

High levels of dopamine

Exploratory behavior, positive emotion, sociability, novelty-seeking, active

• mice genetically engineered to be high in dopamine are very active, explore their cages, eat, and have sex more

Serotonin

• avoidance (stop) system

• Prozac: selective serotonin reuptake inhibitor (SSRI)

  • Physical effect: increases serotonin levels

Low levels of serotonin

Depression, anxiety, obsessive worrying

• Brains firemen —> low levels tells you what stimuli you need, regular levels tells you the problem is fixed

Hormones

Your body’s chemical messengers that travel in bloodstream to tissues or organs (ex. Cortisol)

Cortisol

• glucocorticoid hormone released by adrenal cortex

• Response to stress/threat (fight-flight)

Chronically high cortisol

Anxiety and depression

Chronically low cortisol

Failure to respond to danger

Behavioral Genetics

• examines how genes influence broad patterns of behavior and personality traits

• Complicated history due to associations with eugenics and cloning

Genes amongst people

• ~30k genes stored as DNA sequences within 23 chromosome pairs

• 99% of the genes within the human genome are similar across individuals

• Only 1% make us unique

Inheriting chromosomes

Each person inherits one set of chromosomes from the mother and one set from the father

Genes

Your DNA

Shared environment

The family environment you share with parents and siblings

Non shared environment

Everything else; your unique experiences

Twin studies

• identical (MZ) vs. fraternal twins (DZ)

• Twins reared together vs apart

Adoption studies

Adopted vs. genetically related siblings

Heritability

Amount of variability in personality (phenotype) due to genetic differences (genotype)

How to determine heritability

We can compare personality similarity between

• people who are and are not related (ex. Biological vs. adoptive children)

• People who are related to different degrees (ex. Monozygotic vs dizygotic)

Heritability does not

1. Indicate extent of nature vs. nurture

2. Tell us how genes affect personality

3. Describe genetic contributions to a single individual

4. Indicate whether the effects are generalizable across historical time or populations

5. Imply genetic determinism

Heritability does not indicate extent of nature vs nurture

• traits with little variation will have heritability close to zero

• Heritability coefficients cannot be used to determine what percent of a trait is determined by genetics and by the environment

Heritability does not tell us how genes affect personality

Rather, how genes create propensities to behave in certain ways

Heritability does not describe genetic contributions to a single individual

Heritability refers to the average genetic contribution to individual differences

Heritability does not indicate whether the effects are generalizable across historical time or populations

• heritability always refers to a particular population at a particular time

• If genetic or environmental conditions change, heritability will not remain the same (ex. The heritability of height was lower 100 years ago)

Heritability does not imply genetic determinism

Rather, how genes create propensities to behave in certain ways

Key findings

1. All behavioral traits are at least partially heritable

2. Environment matters (heritability does not equal 1.00)

3. The shared family environment matters much less than genetics

4. Almost half the variability in personality is not due to genes or being raised in the same family (unique experiences not shared by family members)

5. Genetic dispositions are correlated with (and influence) the environment (twins reared apart select and create similar environments)

6. The environment affects biology and genetic expression (aka epigenetics) [many genes are light switches that can be turned on or off]

7. Genes account for both personality stability and change (genes are equally responsible for personality change as the environment)

Myths around candidate genes and personality

• there is no such thing as an extraversion or depression gene

• Traits are polygenic

Conscientiousness is related to which brain system

Self regulation system (standards/control, execution of planned actions)

If your brain is low in dopamine, what might happen

You may have trouble finding the motivation to do things

Why are twin studies useful in studying heritability

Because we can make calculations from the genetic similarity of twins vs other siblings